The Experimental Irradiator Core, which has been in existence since 1986, maintains and operates sources of ionizing radiation for use by Cancer Center members in their experimental studies. Services performed by the resource staff include training in the operation of the sources, advice to users on the design of experiments using radiation, scheduling use of the sources, operating the sources when necessary, dosimetry for new experimental setups, and maintenance and repair of the resources. When not in use by members, these facilities are also available to non-members on an increased-fee basis. The primary resources of the facility are six Cs-137 irradiators. Three Nordion Gammacell 40 irradiators are primarily used for whole body irradiation of rodents or irradiation of attached cultured cells at a constant dose rate: The Shepherd Mark I irradiator is used primarily to deliver radiation to animal tumors or other partialbody irradiations at dose rates comparable to those used in external beam radiotherapy. However, this irradiator can deliver radiation at a broad range of dose rates for a variety of purposes, such as irradiation of cell suspensions or irradiation to high doses to sterilize implant material. The Gammacell 1000 irradiator is used to irradiate suspension cultures at a constant dose rate. The low-dose-rate irradiator, built in-house with a Shepherd 81 source, is used primarily to irradiate cell cultures at dose rates comparable to those used in tumor therapy with radioactive implants, but can deliver radiation at any rate below 2 Gy/hr and has also been used in studies of carcinogenesis from prolonged exposure to low-dose-rate radiation. It is anticipated that in 2008 an in-house-built image-guided small animal radiation research platform (SARRP) will be available to the Core facility. The SARRP is designed to produce the same degree of dose delivery precision in animal models as is currently achievable in human patients.